As electric insulating oils for electrical instruments such as transformers or capacitors, those made of mineral oils containing polychlorinated biphenyls (hereinafter referred to as “PCBs” as the case may be) excellent in electric insulation properties were generally used. However, the toxicity of PCBs to the living body has been confirmed, so that in Japan, the production and import of PCBs have already been prohibited, and use of electric insulating oils and the like that contain PCBs came to be substantially prohibited. However, as it was feared that PCB-containing electric insulating oils and the like that were used in the past may cause environmental pollution in their disposal process, electrical instrument manufacturers or users, industrial waste disposers, and others have been continuing to store the oils and the like, as they are, over a long term up to the present time.
Meanwhile, with the background of the establishment of a safe process for chemically decomposing PCBs, in Japan the so-called PCB special measures law was enacted in 2001. This law obliges to dispose of all PCBs wastes which have been hitherto used or stored, typical examples of which include PCBs-containing electric insulating oils, by July in 2016.
It was initially assumed that PCBs wastes that should be disposed of under the PCB Special Measures Law were limited to those electric insulating oils and the like which had been manufactured or used until production and use of PCBs were prohibited and which had been stored heretofore. However, there were cases where PCBs estimated to be mixed during the production process were detected in electric insulating oils and the like manufactured after prohibition of use of PCBs, and thus some electric insulating oils used at present in electric instruments such as transformers may correspond to PCBs wastes subject to the PCB Special Measures Law. The PCB Special Measures Law set out the time limit as described above, so there has been demand for promptly judging whether electric insulating oils used in existing electric instruments and the like correspond to the PCBs wastes subject to the PCB Special Measures Law (that is, oils and the like containing PCBs at a concentration of not less than 0.5 mg/kg correspond to the PCBs wastes subject to the PCB Special Measures Law, and judgment of whether oils and the like correspond to the PCBs wastes or not is referred to as PCB screening).
It is usually judged based on a result obtained by a high-sensitivity analysis, such as gas chromatography or bioassay, whether or not a sample collected from an object such as an electric insulating oil, contains PCBs at a predetermined concentration. Thus, the sample needs to be subjected to a high-level pretreatment for removing any interfering substance producing an effect on analysis results. Such a pretreatment is usually conducted in accordance with a method described in Appendix No. 2 in Announcement No. 192 issued in 1992 by the Ministry of Health and Welfare of Japan “Method of Testing Standards Concerned with General Wastes Subject to Special Control and Industrial Waste Subject to Special Control” (hereinafter referred to as the “official method”). However, the official method needs a complicated treatment having many steps, such as dimethylsulfoxide (DMSO)/hexane partition, a sulfuric acid treatment, an alkali treatment, and a silica gel column treatment; thus, in order to complete the method, a long period, the length of which is specified by day, is required, and further costs for conducting the method are also very high.
Thus, investigations have been made about a method for pretreating an object to be judged in place of the official method. As a method of extracting polychlorinated biphenyls from an oily liquid such as an electric insulating oil containing PCBs by a simple operation in a short period in order to prepare a sample for analysis, the pamphlet of International Publication WO 2008/123393 discloses a method using a column into which a sulfuric acid silica gel, a metal salt hydrate silica gel (for example, a copper salt hydrate silica gel), a silver nitrate silica gel, and alumina are filled.
However, the metal salt hydrate silica gel or silver nitrate silica gel used in this pretreatment method deteriorates, with the passage of time, after the preparation thereof, so that the capability thereof for removing interfering substances contained in an oily liquid tends to lower. Thus, analysis results of a sample obtained by this pretreatment method may be affected by the interfering substances which remain in the sample.
An object of the present invention is to enhance the level of pretreatment of an oily liquid for which polychlorinated biphenyls contained therein are analyzed.